Background. Some 7.1 million Americans are Myocardial Infarction (MI) survivors. Alabama, a poor state with a high percentage of African Americans and high heart disease mortality, provides an excellent laboratory for increasing guideline adherence. To date, most guideline interventions focus on a single patient condition, but ambulatory post-MI patients are frequently complex, with multiple co-morbidities. Therefore, we propose a randomized trial, MI-plus, to increase physician adherence to guidelines for complex MI patients plus co-morbidities. Objectives. 1) Develop guideline-based performance measures from chart review and administrative data; 2) Identify barriers to physician guideline adherence; 3) Develop and implement an interactive Internet intervention, updated regularly; and 4) Test hypotheses on the intervention's effectiveness, sustainability, and cost-effectiveness. Methods. Together with the state Medicare Peer Review Organization, we will randomize 200 community-based physicians to an intervention or control arm. Our 30-month intervention, customized to the individual physician in real-time, consists of Internet learning modules with case-based education; and performance feedback with benchmarking of practice profiles. We will review medical records and claims data for 3,000 Medicare patients. The main analysis, conducted at the physician level, will compare differential improvement in guideline adherence between the study arms. Ancillary analyses will examine the effects of physician characteristics (e.g., specialty) and patient characteristics (e.g., co-morbidities, ethnicity, gender, age, and socioeconomic status). When appropriate, multivariable techniques will adjust for repeated measures and clustering of patients within physicians. Significance. With a research team that has a proven record of collaboration, this project will produce an evidence-based and replicable cutting-edge intervention that can be sustained in the "real world," readily disseminated, and easily modified for other diseases.